FI81556C - Process for producing hydrogen peroxide - Google Patents

Description

! 81556

Process for the preparation of hydrogen peroxide

It is known that in the so-called anthraquinone method (see the related discussion in Ullmanns Enzyklopädie der 5 techn. Chemie, 4th revised and expanded edition, part 17, pages 697-704) the anthraquinone derivative, a reaction carrier, is dissolved in a solvent or mixture of solvents and the working solution thus obtained is hydrogenated in the presence of a catalyst. In this case, part of the anthraquinone derivative is converted into the corresponding anthrahydroquinone derivative. After filtration of the hydrogenation catalyst, a gas (usually air) is introduced into the working bed, whereupon the hydrogen peroxide forms an anthraquinone derivative.

After the hydrogen peroxide dissolved in the working solution has been extracted with water, the working solution can be passed back to the hydrogenation step. By continuously repeating the individual steps, a circulating process is achieved in which hydrogen peroxide is synthesized from oxygen and hydrogen gases.

Regardless of the technical apparatus used for the extraction of hydrogen peroxide, the extraction step always yields 2 phases, a working solution (raffinate) diluted with respect to the H2 O2 content and an aqueous hydrogen peroxide phase (extract).

Both phases each contain a portion of the other 25 phases dispersed very finely, i.e. the working solution contains small droplets of dilute aqueous hydrogen peroxide, and the aqueous hydrogen peroxide phase contains small amounts of working solution droplets dispersed.

Usually, the working solution phase is passed through commercial coagulators and separators, so-called "water separators", to separate the aqueous dispersed phase. The aqueous phase separated in the "water separators" is a dilute aqueous hydrogen peroxide solution.

35 A number of measures have already been proposed for the purification of aqueous hydrogen peroxide extract.

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Purification of aqueous H 2 O 2 solutions is carried out, for example, by means of an adsorption treatment. The following adsorbents have already been proposed: activated carbon (US-PS 2,919,975). activated carbon in the form of fine charcoal. MgO, freshly doped Al (OH) 3 or Mg (OH) 2 (GB-PS 817 556), activated carbon partially deactivated by adsorption of organic substances inert to H2O2 (DE-PS 15 67 814), ethylene polymer with molecular weight greater than 2000 (GBPS 794 433), water-insoluble, solid, non-polymeric organic substances with molecular weights between about 170-1000 (DE-PS 11 08 191) and porous synthetic resins without chemical functions (DE-OS 17 92 177).

Since the activated carbon decomposes the hydrogen peroxide to be purified, the treatment is preferably carried out at low temperatures. In addition, impurities accumulate in the adsorbents during continuous cleaning, and the adsorbents must be regenerated by means of a special cycle using solvents.

In addition, it is known (US-PS 3,043,666 - FMC) to treat the aqueous H 2 O 2 solution first as a selective solvent for quinone and then to heat the raffinate formed in the presence of a stabilizer until discoloration occurs. The dissolved organic constituents are then oxidized by hydrogen peroxide and then re-extracted and finally distilled. These measures are so cumbersome that use is only worthwhile for special grades.

In other purification methods, the aqueous hydrogen peroxide extract is extracted as a solvent. An inert liquid hydrocarbon having a boiling point at atmospheric pressure not exceeding 145 ° C (DE-AS 10 36 225) or hydrocarbons having a boiling point between 50 and 120 ° C and a solubility in water of less than 0.1% ( JP-PS 35 2361). Even certain chlorinated hydrocarbons have been proposed (DE-AS 11 35 866). Extraction

II

3 81 556 purification processes using low boiling point solvents, solvent residues must be removed from H 2 O 2 after purification; in addition, the contaminated solvent must be regenerated in a separate cycle-5 Rossa - i.e. cumbersome. In addition, many of the proposed solvents have a low flash point.

The disadvantages presented here can be avoided if the purification step is carried out in a solvent mixture consisting of aromatic solvents with a boiling range of 145-10,200 eC (GB-PS 841 323).

In addition, it is known to use a mixture of aromatic hydrocarbons having a boiling point above 145 ° C and methylcyclohexyl acetate in certain proportions for the purification of impure aqueous hydrogen peroxide solutions (DE-AS 14 67 091).

According to the prior art, the extraction of impurities is carried out in spray columns, sieve bottom columns or packed columns by the countercurrent method. In the next step, the entrained solvent droplets are separated from the aqueous phase.

It is known that the diffusion of substances during extraction increases as the phase interface increases; on the other hand, however, the larger the droplets of the dispersed phase, the easier the separation of the biphasic mixture. These two opposing facts lead to a limited result when using column purification based on the extraction of an aqueous hydrogen peroxide solution.

The object of the invention is to separate the dispersed phases as completely as possible from the working solution or the aqueous hydrogen peroxide solution. Another task is to improve the yield of hydrogen peroxide and to reduce the color number and carbon content.

It has now been found that this object can be solved by combining a working solution containing water or an aqueous hydrogen peroxide solution or an aqueous hydrogen peroxide extract 4 81 556 with an aqueous solvent mixture containing hydrogen peroxide stable and less than 1% by volume of water-soluble organic solvents and a mixture thereof. is mixed thoroughly, after which the dispersed phaa-5 si is separated in a separation unit by means of separators.

Preferably, both the phases obtained after extraction with water, i.e. the working solution (raffinate) and the aqueous hydrogen peroxide solution (extract), are treated by the process according to the invention.

10 In addition to water, aqueous hydrogen peroxide solutions can also be added to the working solution. The concentrations of the latter are preferably low. Particularly preferably, the working solution is mixed with water, this is dispersed and then the dispersed aqueous phase is separated from the working solution by means of separators. Water or aqueous hydrogen peroxide solution is added to the working solution in 1-5% by volume of the working solution. Particularly preferably, 1-3% by volume of water is added to the working solution.

Suitable components for the solvent mixture to be added to the hydrogen peroxide extract are, in principle, all quinone solvents known for the anthraquinone process. Quinone solvents refer to both the pure substances intended for this purpose and mixtures of such substances. Usually, a solvent for the quinone that is already present in the working solution is selected. The solvent mixture usually contains 60 to 100% by volume of nonionic solvent and optionally up to 40% by volume of other hydrogen peroxide-stable and minimally water-soluble organic solvents which do not interfere with the production of hydrogen peroxide; in this case, for example, the known hydroquinone solvents for the anthraquinone process and in particular those already present in the working solution. Particularly preferably, the hydrogen peroxide extract is mixed with a solvent mixture which contains practically 100% by volume of a 35 quinone solvent, and which also means a quinone solvent consisting of one substance. A mixture of aromatic gasolines with a boiling range of 180-220 ° C has proved to be particularly suitable as a solvent for quinone.

The solvent mixture is preferably used in an amount of 0.5 to 5% by volume of the amount of hydrogen peroxide extract. With respect to the hydrogen peroxide extract, 1-3% by volume of quinone solvent is particularly preferably added thereto.

Both the aqueous phase and the organic solvent are added to the raffinate or hydrogen peroxide extract formed after the extraction step and mixed with them in conventional mixers; an effective mixture is preferred.

Depending on, inter alia, the structure of the separator used and the fineness of filtration, the most preferred degree of dispersion of the added phase can be easily determined by means of preliminary experiments.

The separation of the dispersed phase in each case is then carried out by means of a separator connected to a suitable separation unit. These separators of ordinary construction, as well as other machine parts, are made of a hydrogen peroxide-resistant material. One, two or more separators may be used. Two or more separators are connected in series in a cross-flow or counter-flow sequence.

Separators of common construction are those described, for example, in Chemical Enhancement Progress, Vol. 59, no. 9, pages 87-88 (1963) and GB Patent 1,427,704. Particularly preferred are separators having a droplet magnifying structure and containing one or more filter layers of glass fiber filament yarn which has been thermally treated. The most advantageous load of the separator, i.e. the amount of dispersion passed through per unit time and filter element, can be determined by a person skilled in the art by means of preliminary tests.

The process according to the invention can be carried out at temperatures of 10-70 ° C, in which case, however, higher or lower temperatures are not excluded. Preferably, the work is carried out at temperatures of 20 to 50 ° C, so that the raffinate and the H 2 O 2 extract can be treated according to the invention at different temperatures.

By using a disproportionate measure per se to dissolve the dispersed phase practically completely, the addition of this phase also improves the washing of hydrogen peroxide from the raffinate on the one hand and the impurities from the extract which would lead to discoloration and too high a degree of carbon content of hydrogen peroxide. The yield of hydrogen peroxide as well as the color and carbon content are substantially improved when using the process according to the invention (Examples 2 and 4).

By raising the dispersed aqueous phase in the raffinate, i.e. the subsequent separation of the dispersed phase in the working solution by means of a separator or separators, it is possible both to improve the total hydrogen peroxide yield and to prevent an increase in the relative humidity of the working solution, see Examples 3 and 4. . Such an effect, namely that the humidity remains constant during implementation, has not been expected in advance.

Relative humidity in this context means the ratio, expressed as a percentage, of the actual moisture content of the continuously circulating working solution to the saturation concentration corresponding to the prevailing temperature of the pure working solution.

Examples 1-4 are shown below. In all 30 examples, the same carrier, namely a mixture of 2-ethylanthraquinone and 2-ethyltetrahydroanthrinone, and the same working solution containing trioctyl phosphate as the solvent for hydroquinone and aromatic gasoline having a boiling range of 35,185-205 ° C as the solvent for quinone are used.

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Example 1 (comparative example according to the prior art)

In the anthraquinone hydrogen peroxide production plant, a packed column is used to purify the aqueous hydrogen peroxide solution from the extraction step, to which hydrogen peroxide and the working solution anthraquinone are countercurrently. The aqueous hydrogen peroxide phase then flows through the column as a dispersed phase from top to bottom, the quinone solvent being passed continuously from bottom to top.

The purification efficiency is expressed as the reduction in carbon content using mg C / l of aqueous crude H 2 O 2 and is 30 mg C / l H 2 O 2 on average when the plant is operating smoothly, while the initial value of unrefined aqueous H 2 O 2 is 220 mg C / l.

Possible disturbances in the operation of the plant will result in an impure product that looks opalescent - slightly cloudy. In this case, it is not possible to remove the turbidity with this purification step, i.e. after 20 purification steps a product is obtained which requires further treatment. In addition, hydrogen peroxide has a very slightly yellowish color due to dissolved chromophores, which gives a color value of 3 in the standard test. To indicate the color value, an aqueous solution of FeCl3 25 is used as calibration solution as follows: Color value_mg FeCl, / l 0 54.0 1 162.6 30 2 270.4 3 378.6

A color comparison in the glass tubes between the hydrogen peroxide phase and the FeCl 3 solutions is then performed.

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Example 2

In the work described in Example 1, a partial flow of aqueous hydrogen peroxide leaving the extraction stage is passed to a separation stage consisting of two successive separation elements comprising a filter layer made of thermally treated fiberglass yarn and layers for enlarging the droplets. To the hydrogen peroxide phase leaving the extraction step, 2 volumes of aromatic gasoline with a boiling range of 182-214 eC per 100 volumes of hydrogen peroxide extract are added countercurrently, the two phases are mixed thoroughly at 20 ° C with a temperature-controlled pump and separated by differential pressure.

The efficiency of the step, again reported in units of 15 mg mg C / l H 2 O 2, is 100-120 mg C / l H 2 O 2, and the initial C content of the solution was the same as in Example 1. The color value measured on the FeCl 3 scale decreases to 0-1.

In the event of any disturbances in the operation of the extraction stage of the apparatus, resulting in a cloudy 20 product, complete purification is always carried out in the separation stage, i.e. the hydrogen peroxide leaving the separation stage is always of uniform and good quality.

Example 3 (comparative example)

In the work described in Example 1, a working solution (raffinate-25 ti) leaving the extraction step is passed to remove the dilute aqueous hydrogen peroxide phase dispersed therein without prior addition of the dispersed phase through a so-called water separator with separation elements.

In each case, after the introduction of a new unit with new elements, a separation of almost 100% of the dispersed aqueous phase is achieved, i.e. the relative humidity of the working solution after the water separation step is 100-102%. Over time, however, the moisture content of the working solution slowly rises from the initial value, i.e., the working solution contains a portion of the indistinguishable dispersed aqueous phase. After about a year il 9 81 556, a relative humidity value of approx. 150-180% is reached, the separating elements must be dismantled and replaced with new elements.

In the case of disturbances which may occur in the extraction step and which lead to an increased formation of the aqueous phase dispersed in the working solution, there is a short-term increase in the relative humidity of up to 300%, depending on the intensity of the disturbance.

Example 4 In the work described in Example 1, about 2% by volume of water relative to the working solution is added to the working solution (raffinate) before the solution enters the separation step and is stirred efficiently. Over a period of operation of more than 12 months, the relative humidity of the working solution leaving the separation step remained at a constant value of 100%. Further treatment of the separated aqueous, slightly hydrogen peroxide-containing phase increases the H 2 O 2 yield by 0.2-0.3%. Also in the case of possible disturbances in the extraction step, the relative humidity in the working solution was always 100% after the separation step. This 20 excellent separation phase activity was also observed even after more than 18 months of operation.

Claims (10)

1. A process for producing hydrogen peroxide according to the so-called. the anthraquinone process, according to which the hydrogen peroxide dissolved in the working solution is extracted by extraction with water and wherein both a reduced hydrogen peroxide working solution as an aqueous hydrogen peroxide extract is obtained, the working solution still contains small amounts of dilute hydrogen peroxide hydroxide aqueous solution. quantities of working solution in dispersed form, which require a subsequent purification, characterized in that a solvent mixture containing organic solvent which is stable to hydrogen is added to the working solution containing water or aqueous hydrogen peroxide, or to the aqueous hydrogen peroxide extract. in water is below 1% by volume and mixes, after which the dispersed phase is separated by a separator in a separator unit. 20 2. A process according to claim 1, characterized in that both the dispersing phase in the working solution and the phase containing the hydrogen peroxide extract are treated according to claim 1. 3. A process according to claims 1 and 2, characterized in that to the working solution is added 1-5% by volume of water or aqueous hydrogen peroxide solution, relative to the working solution. 4. Process according to claims 1 and 2, characterized in that 0.5-5% by volume of solvent mixture is added to the aqueous hydrogen peroxide extract relative to the hydrogen peroxide extract. Process according to claim 1 or 2, characterized in that water containing, or to the aqueous hydrogen peroxide extract containing a working mixture containing practically 100% by volume quinone solvent is added to the working solution and then treated the whole of claim 1 or claim 2. 6. A process according to claim 5, characterized in that 5 to 1% by volume of water is added to the working solution to the working solution. 7. A process according to claim 5, characterized in that adding to the aqueous hydrogen peroxide extract adds 1-3% by volume of quinone solvent in relation to the hydrogen peroxide extract. 10 8. A process according to any one of claims 1, 2, 4, 5 or 7, characterized in that an aromatic gasoline mixture whose boiling point range is 180-220 eC is used as a quinone solvent. 9. A method according to any one of claims 1-8, characterized in that a separator having a droplet-carrying structure is used and which contains one or more filter layers of thermally treated glass filament filament yarn. Method according to any of claims 1-9, characterized in that two successive separators are used.